1. Field of the Invention
The present invention relates to a developing-agent container, a method of manufacturing the developing-agent container, a developing-agent supplying device, and an image forming apparatus.
2. Description of the Related Art
Image forming apparatuses with a developing unit that uses a two-component developing agent including a toner and a magnetic carrier are widely used. In such types of image forming apparatuses, as the toner in the developing agent gets consumed, fresh toner is supplied from a toner container to the developing agent in the developing unit, thus maintaining the concentration of the toner in the developing agent within a predetermined range. However, the carrier in the developing agent remains mostly unconsumed, and is used repeatedly. Consequently, with continued image output, the top layer or the coating layer of the carrier gets abraded or, conversely, toner resin or additive particles adhere to the top layer of the carrier. This results in a progressive decline in the ability of the carrier to charge the toner and a subsequent degradation of the carrier. As the carrier continues to degrade, the charge of the toner diminishes, resulting in banding and toner scattering. Consequently, a maintenance personnel needs to be periodically called to replace the carrier, resulting in increased cost per copy.
Japanese Patent No. 2837309 and Japanese Patent Application Laid-open No. 2004-29306 disclose image forming apparatuses in which a premixed developing agent, which is a mixture of carrier and toner, is added to the developing agent in the developing unit to replenish the concentration of the toner, and surplus developing agent is drained from the developing unit. Spent carrier from the developing agent is drained little by little from the developing unit and fresh carrier in the premixed developing agent is added to the developing agent in the developing unit. Thus, the need for entirely replacing the carrier can be obviated by draining the spent carrier and supplying fresh carrier little by little.
However, before filling the developing-agent container with the premixed developing agent to be supplied to the developing unit, the toner and the carrier are mixed so that the toner particles and the carrier particles are evenly distributed. In spite of that, the proportion of the carrier particles at the bottom of the container tends to be greater accounting for uneven distribution of the toner particles and the carrier particles. This is because a significant amount of air also gets incorporated in the premixed developing agent when it is filled in the developing-agent container. After some time, the bulk of the premixed developing agent settles when the air is expelled from it. During the settling process, the carrier particles sink to the bottom faster than the toner particles because the specific gravity of the carrier particle is greater than that of the toner particle, leading to uneven distribution of the toner particles and the carrier particles.
The developing-agent container now contains a premixed developing agent having unevenly distribution toner particles and carrier particles, and when this premixed developing agent is added to the developing agent in the developing unit, the toner-to-carrier ratio of the premixed developing agent will vary from time to time. If a premixed developing agent having carrier in greater proportion is added to the developing agent, control over toner density will become unsteady leading to a faulty image. If a premixed developing agent having toner in greater proportion is added to the developing agent, the spent carrier in the developing unit fails to be replenished, leading to carrier degradation and therefore a faulty image.
Degradation of even distribution of the toner and the carrier can also pose a problem when the user fits the developing-agent container in the image forming apparatus. Specifically, the user usually shakes the developing-agent container well to obtain evenly distributed toner and carrier before fitting the developing-agent container in the image forming apparatus. The shaking incorporates air in the developing agent within the developing-agent container. However, after some time, the bulk of the developing agent settles by expelling the trapped air. The high specific gravity carrier particles sink to the bottom faster than the low specific gravity toner particles, leading to uneven distribution of the toner particles and the carrier particles.
Uneven distribution of the toner particles and the carrier particles can also result when a toner having a greater specific gravity than the carrier is used, in which case, the proportion of the toner particles at the bottom will be greater.